The objective of this proposal is to investigate the intra-individual reproducibility (within the same individual, when repeatedly measured) and inter-individual variability (among individuals) of glycemic index (Gl) and glycemic load (GL) value determinations for individual foods and food combinations. The specific aims to accomplished this objective are to evaluate reproducibility and variability of Gl value determinations in volunteers differing in biologic characteristics - body mass index (BMI), age and gender;assess the effect of macronutrient amounts and combinations, and fiber on variability of Gl and GL value determinations;assess the effect of prior meal macronutrient composition ('second meal'effect) on Gl value determinations;and relate these data to chronic disease risk factors monitored prior to and during the intervention period. These aims will be accomplished by assessing intra-individual reproducibility and inter-individual variability of repeated Gl value determinations for white bread, commonly used as a reference food, relative to glucose, in volunteers selected to represent a range of BMI's (18.5-24.9, 25-29.9, [unreadable] 30) and ages (18-49.9, 50-85 y), and on the basis of gender, and relate these data to body composition and insulin sensitivity (Phase I). This work will then be extended to address issues related to variability potentially introduced by differences in macronutrient and fiber combinations and loads (Phase II), and finally by 'second meal'effects (Phase III). Prior to each set of food challenges (glucose and test food[s] in random order) volunteers will be characterized on the basis of fasting HbA1c;fructosamine;lipids and lipoproteins;insulin, glucose and C- reactive protein. During the 5-hour challenge (sampling at 0,15, 30, 45, 60, and every 30 minutes thereafter) volunteers will be monitored for changes in blood glucose, insulin, triglycerides, total and high density lipoprotein cholesterol and non-esterified fatty acid levels. The concepts of both Gl and GL are in the public domain and it has been suggested that the concepts be incorporated into U.S. federal dietary guidance (U.S. Dietary Guidelines and Dietary References Intakes [DRI]) formulated to promote health and reduce chronic disease risk. This proposal addresses some of the understudied areas for which additional information would be useful in order to determine whether Gl and GL should be used to classify foods on an individual basis, as has been suggested, and when formulating dietary guidance for the general population.